Process for producing brittle iron plate



Jam, Z39 Q H y, TRASK 2,538,993.

PROCESS FOR PRODUCING BRITTLE IRON PLATE Filed April 6, 1946 Patented Jan. 23, 1951 rares aan PLAT Harold V. Trask, Cooley, Minn., assigner to Boel Metals Qompany, St. Faut, Minn., a corporation Application April 6, 19615, Serial No. 650,039

3 Claims.

This invention relates to the production by electrolysis of readily grindable iron of such com-- position that it is particularly adapted for use, after crushing and annealing, in cold die pressing operations Where substantially pure iron in the form of particles having substantially equi-A aXial structure is required. The present invention is an improvement on the process described and claimed in my application Serial No. 611,947, filed August 22, 1945. The present application is a continuation-in-part of said application.

It is an object of my invention to provide a novel and economical process for producing an iron deposit which is characterized by the presence of a suiiicient quantity of the oxide and hydroxide of iron to render the product readily grindable to particles of sizes suitable for use in iron powder metallurgy and from which the hardening constituents may be removed by simple annealing treatment.

A further object is to provide an improved process for producing brittle iron plate of thc character described by electrolysis of relatively impure, soit iron plates in such manner that economies are effected by reason of the low capi tal investment required in plant and equipment, ease of control in the commercial production of a uniform product and low power consumption per pound of iron produced.

A particular object is to reduce the cost of producing such iron by employing a series arrangement of iron plate electrodes in the elec-- trolyte whereby each plate constitutes a soluble anode at one face and progressively receives a cathode deposit on its opposite face until substantially the entire plate is converted into the required dull, porous iron, thus obviating the need for cathode starting plates.

With these objects in view, immerse a multiplicity of iron plate electrodes in an electrolyte comprising a dilute solution of ferrous chloride such as that described and claimed in my application Serial No. 611,947 and` pass a direct current of suitably low density through the electrodes and solution in series so that each of the electrodes constitutes a soluble anode at one face and receives a porous, brittle cathode deposit on its opposite face. The electrolysis is continued until the original electrodes of impure iron have been dissolved substantially in their entirety and electrcdeposited as relatively pure, brittle, porous iron plates.

My improved iron is sufficiently brittle as deposited at the cathode electrodes to permit economical crushing and contains iron oxides and iron hydroxides together with a small amount of chlorine totaling approximately 3% to 5% of the deposit. This product has a dark gray color and is herein called dull iron plate. Other physical characteristics of my dull iron plate are its hardness, diamond scale, ranging from about 400 to 521),'and its porosity which gives it a specific gravity ranging from approximately 6.3 to 7.25. By crushing or grinding it may be reduced to particles of the desired size (usually minus 100 mesh) of equiaXial structure well adapted for use in iron powder metallurgy. The dull iron plate may be ground in a ball mill with air separation, or in any other suitable grinder or pulverizer at low cost. It may be pulverized to minus 10() mesh sizes in a ball mill at the rate of 20 to 25 pounds per 10o pounds oi balls per hour, Whereas, ordinary electrodeposited iron pulverizes at a rate of from 6.25 to 1.o pounds per 100 pounds of balls per hour. The hardening impurities, oxides and hydroxides may be reduced and the resulting gaseous elements, together with any chlorine carried over from the electrolyte, may be driven off by sirople annealing treatment leaving a product which is more than 99.5% pure iron. The annealing treatment preferably comprises heating the ground product in a hydrogen atmosphere at approximately 80G degrees C. for from one to three hours, depending on the iineness of the product. According to my process for making dull iron plate having the characteristics hereinbefore described, it is essential that the conditions present in the deposition cells with respect to (1) solution composition, (2) current density of the deposition and (3) temperature of deposition, shall be controlled and maintained within the limits presently to be described. The range of permissible values from a technical standpoint must be further limited to minimize the cost of production and facilitate control in commercial operations.

Solution composition An electrolyte comprising a ferrous chloride solution has been found best suited for my purposes. The limits of the solution concentration are from 20 grams to 125 grams of iron per liter of solution and are interrelated with those of the temperature and current density of deposition. For example, the upper limit of iron concentration, as ferrous chloride, in the solution is somewhat dependent on the lowest temperature which can be economically maintained in the cell. 1f, as in most installations, it is not economical to keep the deposition temperature below 15 degrecs C. the maximum concentration of iron is this arrangement the several electrodes Ilia, Ill and b are connected in series so that each of the electrodes l@ constitutes a soluble anode at one face and receives a cathode deposit on its opposite face. At the start of the electrolysis all electrodes are alike and they may comprise ingot iron plates, or other inexpensive iron plates, containing impurities as hereinbefore described. Either the electrode lila or lb, depending on the direction of ow of current, may act as a soluble anode and the other of these terminal electrodes as a cathode which receives the brittle iron deposit at one face only until such time as its position is changed in the cell.

During the electrolysis the concentration of the electrolyte 3 is maintained as hereinbefore described and its pH tends to remain at its required value of from 3 to 5.5. Periodically, if necessary, a small amount of hydrochloric acid may be added. A cell temperature below 40 degrees C. is maintained by circulating cooling liquid through the pipes '5. Current at the density required, preferably from 16 to 13 amperes per square foot, is passed between electrodes in the series arrangement so that the metal from the positive face of each electrode i@ goes into solution and is redeposited upon the negative face of the electrode adjacent to it. The electrolysis may be continued until all of the electrodes iii have been Yconverted into electrodeposited iron of the desired dull gray, brittle and porous char acter. The cathode plate ith, after receiving a deposit of brittle iron, may be reversed and used as the anode l ila during a later cycle of the electrodeposition. By'such procedure all of the electrodes may be converted into brittle deposits of the desired purity. The converted electrodes are nally removed from the cells and separated from their supporting hangers l2. Subsequently they are subjected to grinding and annealing treatment to produce an iron powder of the required structure and purity.

The present process has advantages over other known processes for producing such iron powder which may be summarized as follows:

(l) The power consumption is substantially less than that required for the multiple or parallel circuit arrangement of electrodes in the cells. This is accounted for by the fact that both the carrier bar and bus bar contacts have been subf stantially eliminated, together with the voltage drop and loss of efficiency resulting from such multiple contacts.

(2) Stripping of the brittle iron deposits from the cathodes, which is necessary with the multiple system, is entirely eliminated by the present series arrangement. This results in a saving in labor and eliminates from equipment costs the cost of the flexible cathode starter plates or sheets.

(3) The cost of construction of a commercial plant is further reduced by eliminating the relatively complicated bus bar system and thereby simplifying the plant layout.

(4) Since the power consumption is reduced by the present series system of electrodeposition there is less heating of the electrolyte and a consequent saving in the cost of maintaining the temperature within the required low temperature range.

(5) By the present method I obtain a higher anode recovery and thereby effect a further saving in plant operation cost.

By maintaining the preferred conditions in the cells hereinbefore described, I obtain a porous,

brittle, coherent, dull iron deposit with current efficiencies above 100%. The reasons for this amazingly high enciency are not entirely clear but it is thought that it is at least in part due to the porosity and coherent nature of my cathode deposit. The outer layer of iron as it is formed may act as an intermediate electrode between the anode plate and cathode sheet and electrolysis may cause decomposition of water in the pores between this outer layer and the cathode sheet whereby hydrogen and oxygen are liberated in these pores. Since the outer layer is iron in a very pure form it may combine with the liberated gases to form iron oxide and hydroxide under the conditions existing in the cell. Accordingly, current eliciencies above 100% may indicate that the iron is iirst deposited and later partially altered to the oxide and hydroxide state without affecting the carrying power of the current passing between the anode and cathode. Further substantiation of this theory may be found in the fact that analyses of the dull iron plate show that iron constitutes only from to 97.5% or the product and that the hardening contaminants are oxide and hydroxide compounds which can bev easily removed by annealing in a hydrogen atmosphere.

My coherent dull iron plate may be ground at low cost to sizes suitable for iron powder metallurgy and when finely divided has excellent structure for this purpose in that the individual particies have substantially equiaxial structure rather than a flat structure which results from attempts to grind bright iron deposits. As further hereinbefore pointed out, the ground product may be puried, without destroying its advantageous equiaxial structure, by simple annealing treatment in a hydrogen atmosphere. Analyses of a number of specimens of my dull iron plate show the following ranges of composition in percentages by weight:

Per cent Total cathode iron 95-9'7.5

Cathode chlorine .3-.6 Weight loss after heating in nitrogen at 950 degrees C. for one hour LGO-1.55 Weight loss after heating in ,hydrogen at 950 degrees C. for one hour ZOO-3.55

Total iron after reduction 99.5-99-9 After the crushing and annealing treatment, measured quantities of the powder may be placed in dies and then pressed to the die shape without the application of heat. Pressures of the order of magnitude of 30 to 60 tons per square inch are used. The resulting self-sustaining bodies are then removed from the dies and subjected to a sintering temperature to unite the component iron particles. The bodies so formed from my product have great strength, homogeneous structure and other controlled properties. Test bars formed in this manner from my dull iron plate under 30 tons per square inch pressure and sintered for 11/2 hours at 850 degrees C. have had tensile strength ranging from 23 thousand to 26 thousand pounds per square inch and show elongation under test equal to from 7 to l0 per cent in one inch. It will be evident that the pure iron powder may be mixed with other substances to modify the properties of the end product.

Having described my invention, what I claim as new and desire to protect by Letters Patent is:

1. The process for making brittle, porous iron plate by electrodepostion which comprises, im-

mersing a multiplicity of relatively impure iron plate electrodes in spaced relation one to another` in an electrolyte composed of an aqueous solution of ferrous chloride, passing direct current through the electrodes and solution in series while maintaining the concentration of the solution within the range 20 to 125 grams of iron liter, the pli-1 thereof Within the range 3 to 5.5, the temperature thereof within the range 15 to 40 C., the current density within the range '10 to 40 aiiiperes per square foot, the values within said ranges being selected to produce a brittle, dull gray deposit having speciiic gravity7 from 6.3 to 7.25 and continuing the electrolysis until the several electrodes have been dissolved and redeposited as separate bodies of porous iron.

2. The process for making brittle, porous iron plate by electrodeposition which comprises, immer-sing a multiplicity of relatively impure iron plate electrodes in spaced relation one to another in an electrolyte composed substantially entirely of an aqueous solution of ferrous chloride, passing direct current through the electrodes and solution in series While maintaining the concentration of the solution within the range 50 to plate by electrodeposition which comprises, immersing a multiplicity of relatively impure iron plate electrodes in spaced relation one to another in an electrolyte composed of an aqueous solution of ferrous chloride, passing direct current through the electrodes and solution in series while maintaining the concentration of the so, iution within the range 50 to 87 grams of iron per liter, the pH thereof within the range 3 to 5.5, the temperature thereof approximately at 25 C. and the current density from 16 to 1.8 amperes per square foot and continuing the electrolysis until the several electrodes have been dissolved and redeposited as separate bodies of porous iron.

HAROLD V. TRASK.

REFERENCES CITED The following references are of record in the ffle of this patent:

UNITED STATES PATENTS Number Name Date 377,487 Hayden Feb. 7, 1888 1,456,615 Belcher et al. May 29, 1923 1,912,430 Cain June 6, 1933 1,945,107 Cain Jan. 30, 1934 1,996,342 McGregor Apr. 2, 1935 2,216,167 Fisher Oct. 1, 1940 2,454,168 Balke Mar. 8, 1949 2,464,839 Pike et al Mar. 22, 1949 OTHER REFERENCES vol- 

1. THE PROCESS FOR MAKING BRITTLE, POROUS IRON PLATE BY ELECTRODEPOSITION WHICH COMPRISES, IMMERSING A MULTIPLICITY OF RELATIVELY IMPURE IRON PLATE ELECTRODES IN SPACED RELATION ONE TO ANOTHER IN AN ELECTROLYTE COMPOSED OF AN AQUEOUS SOLUTION OF FERROUS CHLORIDE, PASSING DIRECT CURRENT THROUGH THE ELECTRODES AND SOLUTION IN SERIES WHILE MAINTAINING THE CONCENTRATION OF THE SOLUTION WITHIN THE RANGE 20 TO 125 GRAMS OF IRON PER LITER, THE PH THEREOF WITHIN THE RANGE 3 TO 5.5, THE TEMPERATURE THEREOF WITHIN THE RANGE 15* TO 40* C., THE CURRENT DENSITY WITHIN THE RANGE 10 TO 40 AMPERES PER SQUARE FOOT, THE VALUES WITHIN SAID RANGES BEING SELECTED TO PRODUCE A BRITTLE, DULL GRAY DEPOSIT HAVING SPECIFIC GRAVITY FROM 6.3 TO 7.25 AND CONTINUING THE ELECTROLYSIS UNTIL THE SEVERAL ELECTRODES HAVE BEEN DISSOLVED AND REDEPOSITED AS SEPARATE BODIES OF POROUS IRON. 